Atypical anticipatory postural adjustments during gait initiation among individuals with sub-acute stroke

Abstract

Anticipatory postural adjustments, executed prior to gait initiation, help preserve lateral stability when stepping. Atypical patterns of anticipatory activity prior to gait initiation may occur in individuals with unilateral impairment (e.g., stroke). This study aimed to determine the prevalence, correlates, and consequences of atypical anticipatory postural adjustment patterns prior to gait initiation in a sub-acute stroke population. Forty independently-ambulatory individuals with sub-acute stroke stood on two force plates and initiated gait at a self-selected speed. Medio-lateral centre of pressure displacement was calculated and used to define anticipatory postural adjustments (shift in medio-lateral centre of pressure >10mm from baseline). Stroke severity, motor recovery, and functional balance and mobility status were also obtained. Three patterns were identified: single (typical), absent (atypical), and multiple (atypical) anticipatory postural adjustments. Thirty-five percent of trials had atypical anticipatory postural adjustments (absent and multiple). Frequency of absent anticipatory postural adjustments was negatively correlated with walking speed. Multiple anticipatory postural adjustments were more prevalent when leading with the non-paretic than the paretic limb. Trials with multiple anticipatory postural adjustments had longer duration of anticipatory postural adjustment and time to foot-off, and shorter unloading time than trials with single anticipatory postural adjustments. A high prevalence of atypical anticipatory control prior to gait initiation was found in individuals with stroke. Temporal differences were identified with multiple anticipatory postural adjustments, indicating altered gait initiation. These findings provide insight into postural control during gait initiation in individuals with sub-acute stroke, and may inform interventions to improve ambulation in this population.

Keywords: Gait; Gait initiation; Rehabilitation; Stroke.

Figure 1. Medio-lateral (ML) centre of pressure (COP) and vertical forces during gait initiation

Panel A shows a single APA trial, panel B shows an absent APA trial, and panel C shows a multiple APA trial. Time series’ in the top row of graphs represent ML displacement of the COP, while black and grey time series’ in the bottom row of graphs represent ground reaction forces under the right and left limbs, respectively. Vertical dashed lines represent APA events. APA start time (s) was the time when the ML COP passed the 10 mm threshold (indicated by the horizontal dashed lines). APA end time (e) was the time when the ML COP returned to the 10 mm threshold. Foot-off time (o) was the time when the vertical force under the swing limb was <1% body weight. APA duration was the length of time from APA start to APA end, unloading time was the difference between foot-off time and APA end, and total time to foot-off was the difference between foot-off and APA start.

Figure 2. Relationship between self-selected walking speed and frequency of absent APA trials

Each data point represents a different individual. Note that self-selected walking speed was not available for two individuals. There was a significant moderate correlation between self-selected walking speed and frequency of absent APA trials (Spearman’s correlation coefficient (r)r=−0.53; p=0.0010).